As it is known, it is desirable to re-use waste plastic materials, such as those arising from the disposal of packaging articles or material mixed with food residues in domestic refuse, on order to avoid, or at least to reduce the accumulation of this waste in the nature, and also to slow down the depletion of sources of non-renewable raw materials, in particular the crude oil that goes into the manufacture of plastic materials.
According to the present day techniques, recycling thermoplastic polymers necessitates the separate recovery and re-use of plastic materials of differing chemical nature, because generally they are non miscible with one another and when one tries to re-use mixtures of solid particles of different thermoplastic polymers while using the same machines and the same operation conditions as those employed in the case of a single thermoplastic polymer, articles are obtained which are made of heterogeneous material, of which the mechanical, physical and chemical characteristics, such as the elasticity modulus, the values of tensile strength, flexural strength, compressive strength, resistance to the chemical attack by various liquid or gaseous substances, etc., are not well determined.
In practice, the need for recovering and re-using separately the different thermoplastic polymers places a limitation of an economic order which reduces considerably the possibilities of recycling waste plastic materials, in particular those which are contained in domestic refuse.